1. Field of the Invention
The present invention relates to a hybrid fuel cell system, and more particularly, to an all-in-one hybrid fuel cell system including an electricity generation unit having an electrochemical capacitor capable of reducing a size thereof, having a high power density and a high energy density, and coping with a rapid output change.
2. Description of the Related Art
In general, a fuel cell system is an electricity generating system which directly converts chemical reaction energy of oxygen and hydrogen contained in a hydrocarbon material such as methanol, ethanol, and a natural gas into an electrical energy. The fuel cell is classified into a high temperature fuel cell and a low temperature fuel cell according to an operating temperature.
As examples of the high temperature fuel cell, there are a molten carbonate fuel cell (MCFC), and a solid oxide fuel cell (SOFC). As examples of the low temperature fuel cell, there are an alkaline fuel cell (AFC), a phosphoric acid fuel cell (PAFC), a polymer electrolyte fuel cell (PEMFC), and a direct liquid fuel cell (DLFC).
All the fuel cells are constructed with the same principle. The fuel cells may be classified into various types according to fuel types, operating temperatures, catalysts, electrolytes, and the like.
The polymer electrolyte membrane fuel cell (PEMFC) recently developed has an excellent output characteristic, a low operating temperature, and fast starting and response characteristics. In addition, the polymer electrolyte fuel cell advantageously has a wide range of applications including a mobile power source for vehicles, a distributed power source for home or buildings, and a small-sized power source for electronic apparatuses.
In the polymer electrolyte fuel cell, a fuel pump operates to supply a fuel stored in a fuel tank to a reformer, and the reformer reforms the fuel to generate hydrogen. A stack of the polymer electrolyte fuel cell performs electro-chemical reaction of the hydrogen and oxygen to generate electrical energy. In order to supply the oxygen to the stack, a unit for forcibly fanning an air containing the oxygen may be connected.
The reformer is a unit for generating the hydrogen from the fuel containing the hydrogen through a chemical catalytic reaction using thermal energy. Since the reforming gas generated by the reformer contains a small amount of carbon monoxide (CO) as well as the hydrogen, a unit for removing the carbon monoxide is additionally provided.
Since the direct liquid fuel cell (DLFC) directly uses an organic compound liquid fuel such as methanol and ethanol, the direct liquid fuel cell does not require peripheral units such as a reformer. The direct liquid fuel cell has advantages in easily storing and supplying the fuel and having high energy and electric power densities. A direct liquid fuel cell using methanol as a fuel is called a direct methanol fuel cell (DMFC).
In the direct liquid fuel cell (DLFC), a fuel pump operates to supply a fuel stored in a fuel tank to a stack, and the stack performs an electrochemical reaction of an organic compound liquid fuel such as methanol and oxygen as an oxidant to generate electrical energy. In order to supply the oxygen to the stack, a unit for forcibly fanning an air containing the oxygen is connected.
In the fuel cell system such as a polymer electrolyte fuel cell (PEMFC) and a direct liquid fuel cell (DLFC), the stack which substantially generates electricity includes several to ten stacked unit cells. Each unit cell includes a membrane electrode assembly (MEA) and separators attached on both sides of the membrane electrode assembly. The membrane electrode assembly includes an anode, a cathode, and an electrolyte membrane interposed therebetween.
The separators separate the membrane electrode assemblies. In addition, the separators function as paths for supplying the hydrogen and the oxygen required for the reaction in the fuel cell to the anode and the cathode of the membrane electrode assembly, respectively, and as a conductor for directly connecting the anode and the cathode of the membrane electrode assembly.
Namely, the hydrogen is supplied to the anode through the separators, and the oxygen is applied to the cathode through the separators. In the meantime, an oxidation reaction of the hydrogen by a catalyst occurs in the anode, and a reduction reaction of the oxygen by a catalyst occurs in the cathode. As a result, generated electrons move to generate electricity, and heat and water are generated.
Recently, many attempt to use the fuel cell as a power source for a portable electronic apparatuses such as a mobile phone, a camcorder, and a laptop computer have been made.
As the portable electronic apparatuses for bi-directional communication, satellite mobile communication, a compact disc player, and a laptop computer have high performance, the apparatuses require a high instantaneous pulse power and a high current density. However, there is a problem in that the conventional fuel cell cannot satisfy the requirement. In addition, there is another problem in that the use time of the fuel cell is shortened.
Therefore, in order to supply the high instantaneous pulse power or the high current density required by the portable electronic apparatuses, there has been proposed a capacitor which is separately provided in addition to the fuel cell.
However, the capacitor has shortcomings of a low energy density. In addition, there is a problem in that a whole construction of the apparatus is complicated.